Boulder Lichen

Boulder (Pilophorus acicularis):

Endolithic Crustose Lichen, or boulder lichen, is a highly adaptive variety of lichen that embeds itself in rocks with its body lying above the surface (endolithic). It ranges in color from yellow, orange, red, gray and green. It is inseparable from the surface it grows on, and becomes a problem when it grows on masonry, because removing it will cause damage.